Process for enamelling steel using an electrolytic nickel preplate

ABSTRACT

A novel process for electroplating nickel before enamelling, particularly direct white enamelling, on degreased and pickled steel surfaces.

United States Patent Groschopp et al.

[ 51March 20, 1973 all of Germany Assignee: Henkel & Cie, GmbH, Dusseldorf,

Germany Filed: July 23, 1970 Appl. No.: 57,819

Foreign Application Priority Data Sept. 10, 1969 Germany ..P 19 45 715.9

US. Cl. ..204/38 C, 204/49 Int. Cl. ..C23f 17/00, C23b 5/08 Field of Search ..204/ 38 C, 49

[56] References Cited UNITED STATES PATENTS 875,281 12/1907 McGregor 204/38 C 2,886,498 5/ 1959 Shepard ..204/ 38 C 2,639,264 5/ 1 95 3 Chester ..204/ 38 C 2,351,811 6/1944 Frank ..204/38 C FOREIGN PATENTS OR APPLICATIONS 1,562,616 2/1969 France .204/49 674,490 6/ 1 952 Great Britain ..204/ 3 8 C Primary Examiner-John H. Mack Assistant ExaminerR. L. Andrews Attorney-Hammond & Littell [57] ABSTRACT A novel process for electroplating nickel before enamelling, particularly direct white enamelling, on degreased and pickled steel surfaces.

12 Claims, No Drawings PROCESS FOR ENAMELLING STEEL USING AN ELECTROLYTIC NICKEL PREPLATE STATE OF THE ART Degreasing and pickling of steel surfaces are necessary to prepare the said surfaces for enamelling. However, a nickel coating is usually applied to the said prepared surfaces in order to improve the adhesion of the enamel coating and this is required for a direct white enamelling. Various processes for the degreasing and pickling which give a satisfactory result are known; but, these processes generally require relatively long treatment times of about 20 to 30 minutes. Various attempts have been made to considerably shorten these treatment times by measures such as ultrasonics, electrolytic degreasing and pickling.

The deposition of a suitable nickel layer for enamelling is commercially effected by currentless chemical processes either by an exchange process or a reduction process; but, these processes require a relatively long time of about 6 minutes for a suitable nickel layer. Nickel plating electrolytically has already been attempted to shorten the time for this step to about 60 seconds; but, nickel layers applied electrolytically have not been satisfactory as the adhesion of enamel coatings, particularly direct white enamelling, is substantially better for chemically deposited nickel coatings than for electrolytically deposited coatings.

OBJECTS OF THE INVENTION It is an object of the invention to provide a novel process for the deposition of a nickel layer in a very short time.

It is an other object of the invention to provide a process for the electro deposition of nickel to which an enamel will firmly adhere.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION The novel process of this invention for applying a nickel layer before enamelling comprises passing an electric current at a current density of l to 10 A/dm for less than seconds at a temperature of 45C. to 70C. through an aqueous nickel plating bath containing a water soluble nickel salt and 10 to 60 mg. per liter of a non-ionic surface active agent having a turbidity point below the electroplating temperature to deposit nickel of a degreased and pickled steel surface while cooling at least a portion of the electroplating bath below the turbidity point of the surface-active agent and then reheating the said portion of the bath to the operating temperature. This process provides a uniform nickel layer to which enamel coats will firmly adhere.

To obtain uniform nickel layers, it is necessary to cool the electroplating bath between plating at least partially until it is below the turbidity point of the surface-active agent and then reheating the cooled bath to the operating temperature. The cooled solution may be filtered before re-heating to provide a bath capable of functioning for a longer period of time. Preferably only a portion, such as one-third to one-twentieth per hour, of the electroplating bath is withdrawn and the withdrawal, cooling, heating and re-addition of the electroplating bath is continuous.

The water soluble nickel salts used in the aqueous nickel electroplating baths are those usually used such as nickel sulfate or nickel chloride or mixtures thereof in amounts of 130 to 200 gm per liter for example. The said baths also preferably contain a weak acid such as boric acid to adjust the pH between 3 to 5, preferably 4 to 5. The electroplating baths of the invention preferably do not contain any lustering or leveling agents.

The electroplating baths also contain 10 to 60 mg. per liter of bath of at least one non-ionic surface-active agent having a turbidity point below the operatitlig temperature so that it will form an emulsion in the bath at the operating temperatures. The turbidity point can be easily determined by slowly heating an aqueous solution of the surface-active agent and the first turbidity is easily seen with the eye. The turbidity point preferably is 25C. to 35C. below the operating temperature.

Suitable alkylene oxide adducts for the nickel electrocoating baths of the invention are adducts of the formula Wherein X is selected from the group consisting of oxygen, sulfur or NI-I, R, and R are selected from the group consisting of ethylene and propylene and m, n and p are whole numbers and said adducts form turbid solutions at 45 to C. The said adducts may be polyethylene oxide, polypropylene oxide, mixed adducts of ethylene oxide and propylene oxides and addition products of ethylene oxide and/or propylene oxide with monoor polyvalent, saturated or unsaturated, straight or branch chain, aliphatic, cycloaliphatic, aromatic or heterocyclic alcohols, mercaptans, aldehydes, ketones, acetals, amines, carboxylic acids, carboxylic acid amides and phenols.

A preferred group of adducts of formula I are those inwhich X is oxygen or --Nl-I- and R .andR, are hydrogen or aliphatic, aromatic or aliphatic-aromatic hydrocarbons or an acyl radial of an organic'carboxylic acid of one to 18 carbon atoms. The said adducts where R is other than hydrogen are formed by the addition of two to 300 moles of ethylene oxide and/or propylene oxide with one mole of an alcohol such as aliphatic alcohols of one to 22 carbon atoms such as methanol, butanol, Z-ethybutanol, 2-ethylhexanol, allyl alcohol, oleyl alcohol, etc.; poly-hydroxyl alcohol of two to 22 carbon atoms such asglycol, propanediol, hexanediol, glycerin, erthrite, pentaerythrite, trimethylolpropane,

.sorbitol, polyglycerin, etc.; cycloaliphatic alcohols such as cyclohexanol; aromatic .alcohols such as benzyl alcohol, etc.; monoand poly amines of one to 22 carbon atoms such as ethylamine, ethylene-diamine, triethanolamine, aniline, cyclohexylamine, etc.; aldehydes of l to 22 carbon atoms such as acetaldehyde, myristinaldehyde, benzaldehyde, etc.;-ketones of three to 22 carbon atoms such as acetone, methyl ethyl ketons, acetophenone, etc.; monoand polycarboxylic acids of one to 22 carbon atoms and dimers thereof such as acetic acid, butyric acid, benzoic acid, oxalic acid, adipic acid, phthalic acid, oleic acid, cyclohexanecarboxylic acid, etc.;'and amides of said carboxylic acids such as acetamide, benzamide, etc.; phenols of six to 22 carbon atoms which may be substituted such as phenol, cresol, nonylphenol, naphthol, etc.

In order to make the turbidity point of said adducts fall within the desired temperature range or to decrease the solubility of the adducts in the acid electroplating baths, the terminal hydroxyl group may be replaced with an organic radical R, by different reactions such as reaction with epichlorohydrin or benzylchloride,

esterification with an organic carboxylic acid or acid chloride or other desired method.

Examples of specific adducts useful in the nickel electroplating baths of the invention are polyethyleneoxide with a molecular weight of 30,000, a mixed ethylene oxide-propylene oxide in a 3:1 ratio and having a molecular weight of 10,000, an adduct of 30 moles of propylene oxide and 10 moles of ethylene oxide to 1 mole of propylene glycol, adduct of 30 moles of propylene oxide and 40 moles of ethylene oxide to 1 mole of propylene glycol, adduct of 30 moles of propylene oxide and 9 moles of ethylene oxide to one mole of trimethylolpropane, adduct of 20 moles of ethyleneoxide and 10 moles of propylene oxide to one mole of cetyl alcohol, adduct of 20 moles of ethylene oxide to 1 mole of cetyl alcohol whose terminal hydroxyl group is reacted with epichlorohydrin, adduct of 9 moles of ethylene oxide and 12 moles of propylene oxide to one mole of nonylphenol, adduct of 30 moles of ethylene oxide and 10 moles of propylene oxide to one mole of dimerized fatty acids of linseed oil, adduct of 48 moles of ethylene oxide and 44 miles of propylene oxide to one mole of ethylenediamine, adduct of moles of ethylene oxide to one mole of technical oleyl alcohol whose terminal hydroxy group is acetylated, adduct of propylene oxide to polyglycerin in a ratio of moles of propylene oxide per hydroxy] group, adduct of 10 moles of ethylene oxide and 16 moles of propylene oxide to one mole of hexane-1, 6- diol, adduct of 33 moles of propylene oxide to one mole of trimethylolpropane, adduct of 10 moles of ethylene oxide and 30 moles of propylene oxide to one mole of phenol, etc. The said compounds are merely examples of specific adducts useful for the preparation of nickel deposits. Other adducts can be made by the generally known alkoxylation reaction.

The adducts when added to the acid nickel plating baths have to form free emulsions at'the operating temperatures of 45 to 70C. Some adducts will form clear solutions at room temperatures, said emulsions being seen as turbidity which disappears when the bath is cooled.

The fine emulsions of the adducts in the acid nickel electroplating bath are usually very stable but in some cases it is useful to add up to 2 gm/lit'er of an emulsion stabilizer. Examples of suitable emulsion stabilizers are low molecular weight wetting agents such as branch chained alkyl sulfates or sulfonates, i.e., isohexyl sulfonate, isononyl sulfate, isohexyl sulfate, hexyl sulfate, tetraline sulfonate, isopropylbenzol sulfonate, etc. The amount of stabilizer used should not be higher or the fine emulsion will change into micelluar mixtures. Particularly useful are 0.5 to 1.0 gm/liter of the alkyl sulfates.

The deposition of the nickel coatings is effected at a current density of 1 to 10 A/dm preferably 2 to 5 A/dm, and at these current densities, the operating time is less than 15 seconds; but not usually less than one second and is preferably between 1 to 8 seconds. Longer electroplating times have an unfavorable effect on the adhesion of the enamel coatings.

The process of the invention proves a nickel coating on a steel surface in a very short time which has an unusually good adhesion for the subsequently applied enamel. The total treatment time including degreasing and pickling are greatly shortened. It is even possible to shorten the degreasing and pickling times so greatly that direct white enamelling onto a continuous steel band can also be effected without the coating step being outside a commercially usable time.

1n the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE 1 Steel sheets of decarbonized steel were subjected to alkaline degreasing and intensive pickling after the usual intermediate rinsing. The said plates were given a nickel coating by electroplating with an aqueous bath containing 240 gm of NiSO,-7 H,0 per liter, 50 gm of Ni C1,, 611,0 per liter, gm of boric acid per liter and 30 mg per liter of a water soluble ethylene oxidepropylene oxide adduct having a turbidity point of 22C. in the said bath solution at a current density of 4A/dm and at 50C. for 5 seconds. The plates were then rinsed and made passive with a soda-phosphate solution, dried and direct-white enamelled in the usual way. The enamel coating had a smooth flow and good adhesion. In the standard impact resistance test of DIN 51,155, the enamel coating was the same as an enamel coating done on degreased and pickled steel sheets having a chemically deposited nickel layer requiring a 6 minute operation.

One-fifth by volume of the bath was continuously withdrawn per hour, cooled to 20C. filtered, reheated to 50C. and then continuously re-added to the bath which insured a uniform nickel coating even with prolonged periods of operation in the electroplating bath.

EXAMPLE 2 Using the procedure of Example 1, degreased and pickled steel plates were electroplated using an aqueous nickel electroplating bath containing 280 gm. of

NiSO -7H,O per liter, gm of NiCl,-6H,O per liter, 35 gm of boric acid per liter and 45 mg. per liter of a water soluble ethylene oxide-propylene oxide adduct having a turbidity point of 25C. in the said bath using a current density of 6A/dm' and a temperature of 60 for 2 seconds. The resulting enamel coating had good adhesion and had a smooth flow. 1n the impact resistance test of DIN 51,155, there was no difference between the said sheets and enamelled sheets with a chemical deposit of nickel.

Similar results were obtained by using as the surfaceactive agent, 40 mg. per liter of an adduct of 20 moles of ethylene oxide and 10 moles of propylene oxide with one mole of cetyl alcohol, 30 mg. per liter of an adduct of 9 moles of ethylene oxide and 10 moles of propylene oxide with one mole of nonyl phenol, or 30 mg. per liter of an adduct of 40 moles of ethylene oxide and 40 moles of propylene oxide and one mole of ethylene diamine.

As in Example I, one-fifth by volume of the bath was contineously withdrawn, cooled to 20C., filtered, reheated and re-added to the bath.

EXAMPLE 3 Using the procedure of Example 1, degreased and pickled steel plates were electroplated with an aqueous bath containing 250 gm. of NiSO; 7H O per liter, 50 gm. of NiCl 61-1 per liter, 30 gm. of boric acid per liter and 25 mg. per liter of a water soluble ethylene oxide propylene oxide adduct having a turbiditypoint of 20C. in the said bath of 55C. and a current density of 4A/dm for 2, 5, l0 and 20 seconds, respectively. The adhesion of the enamel layer in the impact resistance test by DIN 51,155 was very good and good for the plates nickel-plated for 2, 5 and seconds but poor for the plate electroplated for 20 seconds.

One-eighth by volume of the bath was withdrawn per hour, cooled to C., filtered and heated to 55C. and added to the bath.

Various modifications of the process and product of the invention may be made without departing from the spirit or scope thereof and it is to be understood that the invention is to be limited only as defined in the appended claims.

We claim:

1. A process for the preparation of a steel surface provided with a direct-white enamel coating which comprises passing an electric current at a cathode current density of l to 10 A/dm for less than l5 seconds at a temperature of 45 to 70C. through an acid aqueous nickelplating bath containing a water-soluble nickel salt and 10 to 60 mg. per liter of a non-ionic surface-active agent having a turbidity point below the electroplating temperature to deposit nickel on a degreased and pickled steel surface and direct-white enamelling said nickel coated steel surfaces, at least a portion of the electroplating bath being continuously withdrawn, cooled below the turbidity point of the surface-active agent and then reheated and readded to the bath.

2. The process of claim 1 wherein the cathode current density is from 2 to 5 A/dm.

3. The process of claim 1 wherein the electro-plating bath contains a weak acid.

4. The process of claim 3 wherein the bath has a pH of 3 to 5.

5. The process of claim 3 wherein the bath has a pH of 4 to 5.

6. The process of claim 3 wherein the weak acid is boric acid.

7. The process of claim 1 wherein the time of electroplating was 1 to 8 seconds.

8. The process of claim 1 wherein the water soluble nickel salt is selected from the group consisting of nickel sulfate, nickel chloride and mixtures thereof.

9. The process of claim 1 wherein the surface active agent is an ethylene oxide-propylene oxide adduct.

10. The process of claim 1 wherein one-third to onetwentieth by volume of the bath is withdrawn per hour, cooled below the turbidity temperature, reheated to the operating turbidity and re-added to the bath.

11. The process of claim 10 wherein the withdrawing, cooling and re-heating steps are effected continuously.

12. The process of claim 1 wherein the cooled withdrawn bath solution is filtered before re-heating. 

2. The process of claim 1 wherein the cathode current density is from 2 to 5 A/dm2.
 3. The process of claim 1 wherein the electro-plating bath contains a weak acid.
 4. The process of claim 3 wherein the bath has a pH of 3 to
 5. 5. The process of claim 3 wherein the bath has a pH of 4 to
 5. 6. The process of claim 3 wherein the weak acid is boric acid.
 7. The process of claim 1 wherein the time of electro-plating was 1 to 8 seconds.
 8. The process of claim 1 wherein the water soluble nickel salt is selected from the group consisting of nickel sulfate, nickel chloride and mixtures thereof.
 9. The process of claim 1 wherein the surface active agent is an ethylene oxide-propylene oxide adduct.
 10. The process of claim 1 wherein one-third to one-twentieth by volume of the bath is withdrawn per hour, cooled below the turbidity temperature, reheated to the operating turbidity and re-added to the bath.
 11. The process of claim 10 wherein the withdrawing, cooling and re-heating steps are effected continuously.
 12. The process of claim 1 wherein the cooled withdrawn bath solution is filtered before re-heating. 